This might sound obvious, but Genshin Impact’s combat centres heavily around elemental abilities, and how you combine them to create powerful reactions that can freeze, melt, or electrocute enemies. How you build and achieve these reactions depends on the combination of characters you have in your party, and how you use their elemental skill, burst, and attacks.
You also need to know how to build characters (opens in new tab) towards their role in your party. Every good team has a healer, a damage-dealer, and some support, whether that means shields, abilities that boost attack, or even create more powerful reactions, as with Anemo characters. Choosing a decent weapon and artifact set isn’t too hard, though, you just need to think about the character’s role in your party. It can also help to read through their talents, as this gives you an idea of what stat their abilities level with, which allows you to prioritise.
Every artifact has a random stat role, so while they provide consistent set-based abilities, they don’t always grant you the most useful stats otherwise. This is why it’s better to invest in levelling artifacts that have good attack-based stat rolls, or are five-star. Weapons are far more straightforward than artifacts—you just want to choose one that has an ability that complements your character’s role. Rely heavily on your elemental skill? Then go with the Sacrificial weapons. Need energy recharge? Go with the Favonius ones.
There are also a good number of decent four-star weapons you can make at the blacksmith, or get through other means, as with The Catch (opens in new tab) in version 2.1.